Исходное сообщение
"Во FreeBSD существенно оптимизированы операции поиска в VFS" Отправлено Аноним, 30-Июл-20 20:04
в новостях о Linux вы тоже говорите что там ногами писано - каждый раз когда там что-то улучшили? * Fast path lookup protected with SMR and sequence counters. 3564           * 3565           * Note: all VOP_FPLOOKUP_VEXEC routines have a comment referencing this one. 3566           * 3567           * Filesystems can opt in by setting the MNTK_FPLOOKUP flag and meeting criteria 3568           * outlined below. 3569           * 3570           * Traditional vnode lookup conceptually looks like this: 3571           * 3572           * vn_lock(current); 3573           * for (;;) { 3574           *      next = find(); 3575           *      vn_lock(next); 3576           *      vn_unlock(current); 3577           *      current = next; 3578           *      if (last) 3579           *          break; 3580           * } 3581           * return (current); 3582           * 3583           * Each jump to the next vnode is safe memory-wise and atomic with respect to 3584           * any modifications thanks to holding respective locks. 3585           * 3586           * The same guarantee can be provided with a combination of safe memory 3587           * reclamation and sequence counters instead. If all operations which affect 3588           * the relationship between the current vnode and the one we are looking for 3589           * also modify the counter, we can verify whether all the conditions held as 3590           * we made the jump. This includes things like permissions, mount points etc. 3591           * Counter modification is provided by enclosing relevant places in 3592           * vn_seqc_write_begin()/end() calls. 3593           * 3594           * Thus this translates to: 3595           * 3596           * vfs_smr_enter(); 3597           * dvp_seqc = seqc_read_any(dvp); 3598           * if (seqc_in_modify(dvp_seqc)) // someone is altering the vnode 3599           *     abort(); 3600           * for (;;) { 3601           *      tvp = find(); 3602           *      tvp_seqc = seqc_read_any(tvp); 3603           *      if (seqc_in_modify(tvp_seqc)) // someone is altering the target vnode 3604           *          abort(); 3605           *      if (!seqc_consistent(dvp, dvp_seqc) // someone is altering the vnode 3606           *          abort(); 3607           *      dvp = tvp; // we know nothing of importance has changed 3608           *      dvp_seqc = tvp_seqc; // store the counter for the tvp iteration 3609           *      if (last) 3610           *          break; 3611           * } 3612           * vget(); // secure the vnode 3613           * if (!seqc_consistent(tvp, tvp_seqc) // final check 3614           *          abort(); 3615           * // at this point we know nothing has changed for any parent<->child pair 3616           * // as they were crossed during the lookup, meaning we matched the guarantee 3617           * // of the locked variant 3618           * return (tvp);